This invention relates generally to a control system of the type wherein manual control devices such as a control stick are provided which have an electro simulated variable rate feel. Hand controller systems having this electro simulated variable rate feel are commonly referred to as active hand controllers. The related inventions referenced hereinbefore utilize electric motors to produce desired hand controller force and position response. These systems require sensors which can provide accurate and stable information about the position of the hand grip and the force or torque exerted upon the hand grip by the operator. The present invention relates specifically to servo motor response in an active hand controller. In the past, servo motor response in an active hand controller has been adversely affected by requirements for large peak motor forces and stable operation with a large null detent, i.e., a large nonlinearity in the force vs. displacement characteristic of the control stick. Control system designers must select several control loop parameters such as integrator time constant, loop gain, proportional gain, damping and motor controller force gain when designing a system. The selection of control loop parameters is made more difficult because the parameters interact and affect one another. In addition, the loop parameters must provide satisfactory operation over a wide range of operating environments. In the past, the parameter selection process typically proceeds by selecting a motor controller force gain to meet the system peak force requirement when the integrator output is near its maximum output. Then by using simulation techniques, analysis, and lab tests the remaining control loop parameters are iteratively selected to achieve the best system response and stability. Once the control designer is satisfied with a particular set of parameters, they are fixed in the design.
Aircraft control systems operate over a wide range of conditions and system performance could be enhanced by modifying the control loop parameters for different conditions. For example when only small system force is required a small motor controller gain could be used and the remaining parameters could be adjusted for fast response. Conversely when peak motor force is required the motor controller gain could be increased and the remaining parameters could be adjusted for stability. Thus a need exists for a servo control system for an aircraft control stick that provides for adjusting the control loop parameters according to operating conditions.